Optical fiber communication system using optical phase conjugation as well as apparatus applicable to the system and method of producing the same

An optical fiber communication system, comprising:

• a first optical fiber having a first end and a second end which correspond to an input end and an output end for a signal beam, respectively;
• a phase conjugator operatively connected to said second end for converting the signal beam into a phase conjugate beam and outputting the phase conjugate beam;
• a second optical fiber having a third end and a fourth end which correspond to an input end and an output end for the phase conjugate beam, respectively;
• at least one dispersion compensator provided on an optical path which includes said first optical fiber, said phase conjugator and said second optical fiber for providing a chromatic dispersion of the opposite sign to that of the chromatic dispersion of each of said first and second optical fibers;
• the product of the average value of the chromatic dispersion and the length of said first optical fiber being substantially coincident with the product of the average value of the chromatic dispersion and the length of said second optical fiber;
• and
• said dispersion compensator which comprises a dispersion compensation fiber having a chromatic dispersion per unit length which is higher in absolute value than that of said second optical fiber.

An optical fiber communication system, comprising:

• a first optical fiber having a first end and a second end which correspond to an input end and an output end for a signal beam, respectively;
• a phase conjugator operatively connected to said second end for converting the signal beam into a phase conjugate beam and outputting the phase conjugate beam;
• a second optical fiber having a third end and a fourth end which correspond to an input end and an output end for the phase conjugate beam, respectively the product of the average value of the chromatic dispersion and the length of said first optical fiber being substantially coincident with the product of the average value of the chromatic dispersion and the length of said second optical fiber;
• the signal beam being a wavelength division multiplexed signal beam including a plurality of signal beams having wavelengths different from each other;
• both of the second-order dispersions (dispersion gradients) of said first and second optical fibers being substantially equal to zero or having signs opposite to each other;
• and
• a dispersion compensator which comprises a dispersion compensation fiber having a chromatic dispersion per unit length which is higher in absolute value than that of said second optical fiber.

An apparatus for generating phase conjugate light, comprising:

• a nonlinear optical medium having a first end and a second end, said first end being supplied with signal light;
• a pump light source for supplying pump light from at least one of said first end and said second end into said nonlinear optical medium;
• a first optical band block filter operatively connected to said second end of said nonlinear optical medium and having a block band including the wavelength of the pump light;
• and
• a second optical band block filter operatively connected to said first end of said nonlinear optical medium and having a block band including the wavelength of phase conjugate beam generated in said nonlinear optical medium.

An optical transmission apparatus connected to an input end of an optical fiber transmission line, comprising:

• a first optical fiber having an input end-and an output end and having a chromatic dispersion amount substantially equal to a chromatic dispersion amount between a midpoint and said input end of said optical fiber transmission line;
• optical signal outputting means for inputting an optical signal to said input end of said first optical fiber;
• a phase conjugator for converting the optical signal from said output end of said first optical fiber into phase conjugate light which has a phase conjugate relationship with the optical signal and inputting the phase conjugate light to said input end of said optical transmission line;
• and
• said first optical fiber includes a dispersion decreasing fiber having a chromatic dispersion which decreases as power of a signal beam decreases.

An optical reception apparatus connected to an output end of an optical fiber transmission line which transmits an optical signal, comprising:

• a second optical fiber having an input end and an output end and having a chromatic dispersion amount substantially equal to a chromatic dispersion amount between a midpoint and said output end of said optical fiber transmission line;
• a phase conjugator for converting the optical signal received from said optical fiber transmission line into phase conjugate light which has a phase conjugate relationship with the optical signal and inputting the phase conjugate light into said input end of said second optical fiber;
• a receiver for receiving the phase conjugate light from said output end of said second optical fiber, and
• a dispersion compensator which comprises a dispersion compensation fiber having a chromatic dispersion per unit length which is higher in absolute value than that of said second optical fiber.

An optical communication system including an optical transmission apparatus connected to an input end of an optical fiber transmission line, and an optical reception apparatus connected to an output end of said optical fiber transmission line,

• said optical transmission apparatus comprising:
• a first optical fiber having an input end and an output end and having a chromatic dispersion amount substantially equal to a chromatic dispersion amount between a midpoint and said input end of said optical fiber transmission line;
• optical signal outputting means for inputting an optical signal to said input end of said first optical fiber;
• and
• a first phase conjugator for converting the optical signal from said output end of said first optical fiber into first phase conjugate light which has a phase conjugate relationship with the optical signal and inputting the first phase conjugate light to said input end of said optical transmission line;
• said optical reception apparatus comprising:
• a second optical fiber having an input end and an output end and having a chromatic dispersion value substantially equal to a chromatic dispersion amount between said midpoint and said output end of said optical fiber transmission line;
• a second phase conjugator for converting the first phase conjugate light received from said optical fiber transmission line into second phase conjugate light which has a phase conjugate relationship with the phase conjugate light and inputting the second phase conjugate light into said input end of said second optical fiber;
• a receiver for receiving the second phase conjugate light from said output end of said second optical fiber;
• and
• a dispersion compensator which comprises a dispersion compensation fiber having a chromatic dispersion per unit length which is higher in absolute value than that of said second optical fiber.

An optical fiber communication system, comprising:

• a first optical fiber having a first end and a second end which correspond to an input end and an output end for a signal beam, respectively;
• a first phase conjugator operatively connected to said second end for converting the signal beam into a first phase conjugate beam and outputting the first phase conjugate beam;
• a second optical fiber having a third end and a fourth end which correspond to an input end and an output end for the first phase conjugate beam, respectively;
• a second phase conjugator operatively connected to said fourth end for converting the first phase conjugate beam into a second phase conjugate beam and outputting the second phase conjugate beam;
• and
• a third optical fiber having a fifth end and a sixth end which correspond to an input end and an output end for the second phase conjugate beam;
• said second optical fiber comprising a first portion located between said third end and a system midpoint and a second portion located between said system midpoint and said fourth end;
• the product of the average value of the chromatic dispersion and the length of said first optical fiber being substantially coincident with the product of the average value of the chromatic dispersion and the length of said first portion;
• the product of the average value of the chromatic dispersion and the length of said second portion being substantially coincident with the product of the average value of the chromatic dispersion and the length of said third optical fiber;
• and
• a branching unit provided in the proximity of said system midpoint of said second optical fiber for branching the first phase conjugate beam into a plurality of branch beams,
• each of said second portion, said second phase conjugator and said third optical fiber being provided by a plural number corresponding to the plurality of branch beams,
• the plurality of branch beams being individually supplied to the plurality of second portions.

An optical fiber communication system, comprising:

• a first optical fiber having a first end and a second end which correspond to an input end and an output end for a signal beam, respectively;
• a first phase conjugator operatively connected to said second end for converting the signal beam into a first phase conjugate beam and outputting the first phase conjugate beam;
• a second optical fiber having a third end and a fourth end which correspond to an input end and an output end for the first phase conjugate beam, respectively;
• a second phase conjugator operatively connected to said fourth end for converting the first phase conjugate beam into a second phase conjugate beam and outputting the second phase conjugate beam;
• and
• a third optical fiber having a fifth end and a sixth end which correspond to an input end and an output end for the second phase conjugate beam;
• said second optical fiber comprising a first portion located between said third end and a system midpoint and a second portion located between said system midpoint and said fourth end;
• the product of the average value of the chromatic dispersion and the length of said first optical fiber being substantially coincident with the product of the average value of the chromatic dispersion and the length of said first portion;
• the product of the average value of the chromatic dispersion and the length of said second portion being substantially coincident with the product of the average value of the chromatic dispersion and the length of said third optical fiber;
• and
• said first optical fiber includes a dispersion decreasing fiber having a chromatic dispersion which decreases as the power of the signal beam decreases, whereby the ratio between the product of the optical power and the nonlinear coefficient and the chromatic dispersion of said first optical fiber is substantially constant.

An optical fiber communication system, comprising:

• a first optical fiber having a first end and a second end which correspond to an input end and an output end for a signal beam, respectively;
• a first phase conjugator operatively connected to said second end for converting the signal beam into a first phase conjugate beam and outputting the first phase conjugate beam;
• a second optical fiber having a third end and a fourth end which correspond to an input end and an output end for the first phase conjugate beam, respectively;
• a second phase conjugator operatively connected to said fourth end for converting the first phase conjugate beam into a second phase conjugate beam and outputting the second phase conjugate beam;
• and
• a third optical fiber having a fifth end and a sixth end which correspond to an input end and an output end for the second phase conjugate beam;
• said second optical fiber comprising a first portion located between said third end and a system midpoint and a second portion located between said system midpoint and said fourth end;
• the product of the average value of the chromatic dispersion and the length of said first optical fiber being substantially coincident with the product of the average value of the chromatic dispersion and the length of said first portion;
• the product of the average value of the chromatic dispersion and the length of said second portion being substantially coincident with the product of the average value of the chromatic dispersion and the length of said third optical fiber;
• and
• at least one dispersion compensator provided at the input end or the output end or intermediately of at least one of said first, second and third optical fibers for providing a chromatic dispersion of the opposite sign to that of the chromatic dispersion of each of said first, second and third optical fibers, wherein
• said dispersion compensator comprises a dispersion compensation fiber having a chromatic dispersion per unit length which is higher in absolute value than that of said second optical fiber.

An optical fiber communication system, comprising:

• a first optical fiber having a first end and a second end which correspond to an input end and an output end for a signal beam, respectively;
• a first phase conjugator operatively connected to said second end for converting the signal beam into a first phase conjugate beam and outputting the first phase conjugate beam;
• a second optical fiber having a third end and a fourth end which correspond to an input end and an output end for the first phase conjugate beam, respectively;
• a second phase conjugator operatively connected to said fourth end for converting the first phase conjugate beam into a second phase conjugate beam and outputting the second phase conjugate beam;
• and
• a third optical fiber having a fifth end and a sixth end which correspond to an input end and an output end for the second phase conjugate beam;
• said second optical fiber comprising a first portion located between said third end and a system midpoint and a second portion located between said system midpoint and said fourth end;
• the product of the average value of the chromatic dispersion and the length of said first optical fiber being substantially coincident with the product of the average value of the chromatic dispersion and the length of said first portion;
• the product of the average value of the chromatic dispersion and the length of said second portion being substantially coincident with the product of the average value of the chromatic dispersion and the length of said third optical fiber;
• and
• at least one dispersion compensator provided at the input end or the output end or intermediately of at least one of said first, second and third optical fibers for providing a chromatic dispersion of the opposite sign to that of the chromatic dispersion of each of said first, second and third optical fibers, wherein
• each of said first, second and third optical fibers provides a normal dispersion, and said dispersion compensator comprises a 1.3 μm zero dispersion fiber.

An optical fiber communication system, comprising:

• a first optical fiber having a first end and a second end which correspond to an input end and an output end for a signal beam, respectively;
• a first phase conjugator operatively connected to said second end for converting the signal beam into a first phase conjugate beam and outputting the first phase conjugate beam;
• a second optical fiber having a third end and a fourth end which correspond to an input end and an output end for the first phase conjugate beam, respectively;
• a second phase conjugator operatively connected to said fourth end for converting the first phase conjugate beam into a second phase conjugate beam and outputting the second phase conjugate beam;
• and
• a third optical fiber having a fifth end and a sixth end which correspond to an input end and an output end for the second phase conjugate beam;
• said second optical fiber comprising a first portion located between said third end and a system midpoint and a second portion located between said system midpoint and said fourth end;
• the product of the average value of the chromatic dispersion and the length of said first optical fiber being substantially coincident with the product of the average value of the chromatic dispersion and the length of said first portion;
• the product of the average value of the chromatic dispersion and the length of said second portion being substantially coincident with the product of the average value of the chromatic dispersion and the length of said third optical fiber;
• and
• at least one dispersion compensator provided at the input end or the output end or intermediately of at least one of said first, second and third optical fibers for providing a chromatic dispersion of the opposite sign to that of the chromatic dispersion of each of said first, second and third optical fibers, wherein
• said dispersion compensator comprises a fiber grating.

An apparatus for generating phase conjugate light, comprising:

• a nonlinear optical medium having a first end and a second end, said first end being supplied with signal light;
• a pump light source for supplying pump light from at least one of said first end and said second end into said nonlinear optical medium;
• an optical band block filter operatively connected to said second end of said nonlinear optical medium and having a block band including the wavelength of the pump light;
• said nonlinear optical medium includes an optical fiber which has a nonlinear coefficient sufficiently high to make the length of said optical fiber short to such a degree that said optical fiber has a polarization plane maintaining capacity;
• and
• wherein said optical fiber comprises a single mode fiber, and said single mode fiber has a mode field diameter smaller than the mode field diameter of a single mode fiber which is used as a transmission line.

An optical fiber communication system, consisting of:

• a first optical fiber having a first end and a second end which correspond to an input end and an output end for a signal beam, respectively;
• a first phase conjugator operatively connected to said second end for converting the signal beam into a first phase conjugate beam and outputting the first phase conjugate beam;
• a second optical fiber having a third end and a fourth end which correspond to an input end and an output end for the first phase conjugate beam, respectively;
• a second phase conjugator operatively connected to said fourth end for converting the first phase conjugate beam into a second phase conjugate beam and outputting the second phase conjugate beam;
• and
• a third optical fiber having a fifth end and a sixth end which correspond to an input end and an output end for the second phase conjugate beam;
• said second optical fiber comprising a first portion located between said third end and a system midpoint and a second portion located between said system midpoint and said fourth end;
• the product of the average value of the chromatic dispersion and the length of said first optical fiber being substantially coincident with the product of the average value of the chromatic dispersion and the length of said first portion;
• the product of the average value of the chromatic dispersion and the length of said second portion being substantially coincident with the product of the average value of the chromatic dispersion and the length of said third optical fiber.